Process for reforming NAPHTHA feedstock using selective multimetallic-multigradient reforming catalyst

ABSTRACT

A novel catalyst and the use thereof in a reforming process is disclosed. The dual-function catalyst comprises a refractory inorganic oxide, indium, Group IVA(IUPAC 14) metal, and a platinum-group metal concentrated in the surface layer of each catalyst particle. Utilization of this catalyst in the conversion of hydrocarbons, especially in reforming, results in significantly improved selectivity to the desired gasoline or aromatics product.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a division of prior application Ser. No. 08/840,562now U.S. Pat. No. 5,858,908, filed Apr. 17, 1997, the contents of whichare incorporated herein by reference thereto.

FIELD OF THE INVENTION

This invention relates to an improved catalyst for the conversion ofhydrocarbons, and more specifically for the catalytic reforming ofgasoline-range hydrocarbons.

BACKGROUND OF THE INVENTION

The subject of the present invention is a novel dual-function catalyticcomposite, characterized by a combination of three or more metals withspecified gradients on the finished catalyst particle, and its use inhydrocarbon conversion. Catalysts having both ahydrogenation-dehydrogenation function and an isomerization/crackingfunction ("dual-function" catalysts) are used widely in manyapplications, particularly in the petroleum and petrochemical industry,to accelerate a wide spectrum of hydrocarbon-conversion reactions. Theisomerization/cracking function generally relates to an acid-actionmaterial of the porous, adsorptive, refractory-oxide type which istypically utilized as the support or carrier for a heavy-metalcomponent, such as the Group VIII(IUPAC 8-10) metals, which primarilycontribute the hydrogenation-dehydrogenation function. Other metals incombined or elemental form can influence one or both of theisomerization/cracking and hydrogenation-dehydrogenation functions.

In another aspect, the present invention comprehends improved processesthat emanate from the use of the novel catalyst. These dual-functioncatalysts are used to accelerate a wide variety ofhydrocarbon-conversion reactions such as dehydrogenation, hydrogenation,hydrocracking, hydrogenolysis, desulfurization, cyclization, catalyticcracking, alkylation, polymerization, and isomerization. In a specificaspect, an improved reforming process utilizes the subject catalyst toincrease selectivity to gasoline and aromatics products.

Catalytic reforming comprises a variety of reaction sequences, includingdehydrogenation of cyclohexanes to aromatics, dehydroisomerization ofalkylcyclopentanes to aromatics, dehydrocyclization of an acyclichydrocarbon to aromatics, hydrocracking of paraffins to light productsboiling outside the gasoline range, dealkylation of alkylbenzenes andisomerization of paraffins. Some of the reactions occurring duringreforming, such as hydrocracking which produces light paraffin gases,have a deleterious effect on the yield of products boiling in thegasoline range. Improvements in catalytic reforming technology thus aretargeted toward enhancing those reactions effecting a higher yield ofthe gasoline fraction at a given octane number.

It is of critical importance that a dual-function catalyst exhibit thecapability both to initially perform its specified functions efficientlyand to perform them satisfactorily for prolonged periods of time. Theparameters used in the art to measure how well a particular catalystperforms its intended functions in a particular hydrocarbon reactionenvironment are activity, selectivity and stability. In a reformingenvironment, these parameters are defined as follows:

Activity is a measure of the ability of the catalyst to converthydrocarbon reactants to products at a designated severity levelrepresenting a combination of reaction conditions: temperature,pressure, contact time, and hydrogen partial pressure. Activitytypically is designated as the octane number of the pentanes and heavier("C₅ +") product stream from a given feedstock at a given severitylevel, or conversely as the temperature required to achieve a givenoctane number.

Selectivity refers to the percentage yield of petrochemical aromatics orC₅ + gasoline product from a given feedstock at a particular activitylevel.

Stability refers to the rate of change of activity or selectivity perunit of time or of feedstock processed. Activity stability generally ismeasured as the rate of change of operating temperature per unit oftime/feedstock to achieve a given C₅ + product octane, with a lower rateof change corresponding to better activity stability. Selectivitystability is measured as the rate of decrease of C₅ + product oraromatics yield per unit of time or of feedstock.

Research and development to improve performance of reforming catalystsis being stimulated by the reformulation of gasoline, following uponwidespread removal of lead antiknock additive, in order to reduceharmful vehicle emissions. Gasoline-upgrading processes such ascatalytic reforming must operate at higher efficiency with greaterflexibility in order to meet these changing requirements. Catalystselectivity is becoming ever more important to tailor gasolinecomponents to these needs while avoiding losses to lower-value products.The major problem facing workers in this area of the art, therefore, isto develop more selective catalysts while maintaining effective catalystactivity and stability.

The art teaches the use of indium in multimetallic catalysts for thecatalytic reforming of naphtha feedstocks. U.S. Pat. No. 3,951,868(Wilhelm) teaches a catalyst comprising platinum, halogen, germanium ortin, and indium wherein the ratio of indium to platinum-group metal isabout 0.1:1-1:1. U.S. Pat. No. 4,522,935 (Robinson et al.) discloses acatalyst comprising a platinum-group metal, tin, indium, a halogen, anda porous support which may comprise alumina. The feature of the catalystis an atomic ratio of indium to platinum-group metal of more than 1.35,and preferably about 2.55. Neither of these references suggest amultigradient catalyst in which the platinum-group metal is concentratedin the surface layer.

U.S. Pat. No. 4,786,625 (Imai et al.) teaches a dehydrogenation catalystcomprising a surface-impregnated platinum-group metal and a modifierselected from tin, germanium and rhenium on a refractory support havinga nominal diameter of at least 850 microns. The catalyst preferably isnonacidic to minimize isomerization activity through incorporation of analkali or alkaline earth metal.

SUMMARY OF THE INVENTION

It is an object of the invention to provide a novel catalyst forimproved selectivity in hydrocarbon conversion. A corollary object ofthe invention is to provide a reforming process having improvedselectivity with respect to gasoline or aromatics yields.

The invention originates from the discovery that a dual-functioncatalyst containing surface-layer platinum and uniformly dispersed tinand indium on chlorided alumina shows improved yields of C₅ + product ina reforming reaction.

A broad embodiment of the present invention is a dual-function catalystcomprising a refractory inorganic oxide and a multigradient metalcomponent comprising indium, a Group IVA(IUPAC 14) metal, and aplatinum-group metal which is present in a catalyst particle as asurface-layer component. The Group IVA metal and indium preferably areuniformly dispersed in the catalyst particle. The catalyst optimallyalso comprises a halogen component, especially chlorine. In preferredembodiments the refractory inorganic oxide is alumina, theplatinum-group metal is platinum, and the Group IVA metal is tin. Ahighly preferred catalyst comprises uniformly dispersed tin and indiumand surface-layer platinum.

In another aspect, the invention is a process for the conversion of ahydrocarbon feedstock utilizing the present catalyst. Preferably thehydrocarbon conversion is catalytic reforming of a naphtha feedstock,utilizing the catalyst of the invention to increase the yield ofgasoline and/or aromatics. The conversion more preferably comprisesdehydrocyclization to increase aromatics yields.

These as well as other objects and embodiments will become evident fromthe following detailed description of the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows the concentration of platinum and tin across the radius ofspherical particles of Catalyst A.

FIG. 2 shows the concentration of platinum, indium and tin across theradius of spherical particles of Catalyst X.

FIG. 3 shows a comparison of C₅ + yield vs. conversion for Catalysts Aand X.

FIG. 4 shows the concentration of platinum and tin across the radius ofspherical particles of Catalyst B.

FIG. 5 shows the concentration of platinum and tin across the radius ofspherical particles of Catalyst C.

FIG. 6 shows the concentration of platinum, indium and tin across theradius of spherical particles of Catalyst Y.

FIG. 7 shows the concentration of platinum, indium and tin across theradius of spherical particles of Catalyst Z.

FIG. 8 shows a comparison of C₅ + yield vs. conversion for Catalysts Band Y.

FIG. 9 shows a comparison of C₅ + yield vs. conversion for Catalysts Cand Z.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

A broad embodiment of the present invention, therefore, is adual-function catalyst comprising a refractory inorganic-oxide supportand a multigradient metal component comprising indium, at least onemetal of Group IVA(IUPAC 14) of the Periodic Table [See Cotton andWilkinson, Advanced Inorganic Chemistry, John Wiley & Sons (FifthEdition, 1988)] and a surface-layer platinum-group metal. In anotheraspect, the invention embraces the use of the present catalyst inhydrocarbon conversion and especially in a reforming process.

The refractory support utilized in the present invention usually is aporous, adsorptive, high-surface area support having a surface area ofabout 25 to about 500 m² /g. The porous carrier material should also beuniform in composition and relatively refractory to the conditionsutilized in the hydrocarbon conversion process. By the terms "uniform incomposition" it is meant that the support be unlayered, has noconcentration gradients of the species inherent to its composition, andis completely homogeneous in composition. Thus, if the support is amixture of two or more refractory materials, the relative amounts ofthese materials will be constant and uniform throughout the entiresupport. It is intended to include within the scope of the presentinvention carrier materials which have traditionally been utilized indual-function hydrocarbon conversion catalysts such as:

(1) refractory inorganic oxides such as alumina, magnesia, titania,zirconia, chromia, zinc oxide, thoria, boria, silica-alumina,silica-magnesia, chromia-alumina, alumina-boria, silica-zirconia, etc.;

(2) ceramics, porcelain, bauxite;

(3) silica or silica gel, silicon carbide, clays and silicates which aresynthetically prepared or naturally occurring, which may or may not beacid treated, for example attapulgus clay, diatomaceous earth, fuller'searth, kaolin, or kieselguhr;

(4) crystalline zeolitic aluminosilicates, such as X-zeolite, Y-zeolite,mordenite, β-zeolite, Ω-zeolite or L-zeolite, either in the hydrogenform or most preferably in nonacidic form with one or more alkali metalsoccupying the cationic exchangeable sites;

(5) non-zeolitic molecular sieves, such as aluminophosphates orsilico-alumino-phosphates; and

(6) combinations of one or more materials from one or more of thesegroups.

Preferably the refractory support comprises one or more inorganicoxides, with the preferred refractory inorganic oxide for use in thepresent invention being alumina. Suitable alumina materials are thecrystalline aluminas known as the gamma-, eta-, and theta-alumina, withgamma- or eta-alumina giving best results. The preferred refractoryinorganic oxide has an apparent bulk density of about 0.3 to about 1.0g/cc and surface-area characteristics such that the average porediameter is about 20 to 300 angstroms, the pore volume is about 0.1 toabout 1 cc/g, and the surface area is about 100 to about 500 m² /g.Optimally the refractory inorganic oxide comprise substantially pureZiegler alumina as described hereinbelow having an apparent bulk densityof about 0.6 to about 1 g/cc, a pore volume of 0.3 to 0.8 cc/g) andsurface area of about 150 to 280 m² /g (preferably 185 to 235 m² /g).

Considering that alumina is the preferred refractory inorganic oxide, aparticularly preferred alumina is that which has been characterized inU.S. Pat. Nos. 3,852,190 and 4,012,313 as a by-product from a Zieglerhigher alcohol synthesis reaction as described in Ziegler's U.S. Pat.No. 2,892,858, hereinafter referred to as a "Ziegler alumina". Ziegleralumina is presently available from the Vista Chemical Company under thetrademark "Catapal" or from Condea Chemie GmbH under the trademark"Pural," and will be available from ALCOA under the trademark "HiQ-20."This high-purity pseudoboehmite, after calcination at a hightemperature, has been shown to yield a gamma-alumina of extremely highpurity.

The alumina powder can be formed into any desired shape or type ofcarrier material known to those skilled in the art such as spheres,rods, pills, pellets, tablets, granules, extrudates, and like forms bymethods well known to the practitioners of the catalyst material formingart.

The preferred form of the present catalyst support is a sphere, with apreferred diameter of between about 0.7 mm and 3.5 mm. Alumina spheresmay be continuously manufactured by the well known oil-drop method whichcomprises: forming an alumina hydrosol by any of the techniques taughtin the art and preferably by reacting aluminum metal with hydrochloricacid; combining the resulting hydrosol with a suitable gelling agent;and dropping the resultant mixture into an oil bath maintained atelevated temperatures. The droplets of the mixture remain in the oilbath until they set and form hydrogel spheres. The spheres are thencontinuously withdrawn from the oil bath and typically subjected tospecific aging and drying treatments in oil and an ammoniacal solutionto further improve their physical characteristics. The resulting agedand gelled particles are then washed and dried at a relatively lowtemperature of about 150° to about 205° C. and subjected to acalcination procedure at a temperature of about 450° to about 700° C.for a period of about 1 to about 20 hours. This treatment effectsconversion of the alumina hydrogel to the corresponding crystallinegamma-alumina. U.S. Pat. No. 2,620,314 provides additional details andis incorporated herein by reference thereto.

An alternative form of carrier material is a cylindrical extrudate,preferably prepared by mixing the alumina powder with water and suitablepeptizing agents such as HCl until an extrudable dough is formed. Theamount of water added to form the dough is typically sufficient to givea loss on ignition (LOI) at 500° C. of about 45 to 65 mass-%, with avalue of 55 mass-% being preferred. The acid addition rate is generallysufficient to provide 2 to 7 mass-% of the volatile-free alumina powderused in the mix, with a value of 3 to 4 mass-% being preferred. Theresulting dough is extruded through a suitably sized die to formextrudate particles. These particles are then dried at a temperature ofabout 260° to about 427° C. for a period of about 0.1 to 5 hours to formthe extrudate particles. The preferred diameter of cylindrical extrudateparticles is between about 0.7 and 3.5 mm, with a length-to-diameterratio of between about 1:1 and 5:1.

An essential component of the present catalyst is a multigradient metalcomponent comprising indium, a Group IVA (IUPAC 14) metal, and aplatinum-group metal. "Multigradient" designates the differingdistribution of two or more metals in particles of the catalyst,particularly the concentration of metal as measured between the externalsurface and the central core of such particles. Preferably the indiumand Group IVA metal are uniformly distributed throughout the catalystparticle, although it is within the scope of the invention that thesetwo metal components have differing distributions. The platinum-groupmetal is present in the catalyst particles as a "surface-layer"component. A metal "component" refers to the metal as a complexcombination with the carrier or other catalyst components, in combinedform and/or in the elemental state.

Indium is an essential component of the multi-gradient metal componentof the present catalyst. The indium may be present in the catalyticcomposite in any catalytically available form such as the elementalmetal, a compound such as the oxide, hydroxide, halide, oxyhalide,aluminate, or in chemical combination with one or more of the otheringredients of the catalyst. Although not intended to so restrict thepresent invention, it is believed that best results are obtained whenthe indium is present in the composite in a form wherein substantiallyall of the indium moiety is in an oxidation state above that of theelemental metal such as in the form of the oxide, oxyhalide or halide orin a mixture thereof and the subsequently described oxidation andreduction steps that are preferably used in the preparation of theinstant catalytic composite are specifically designed to achieve thisend.

Indium can be present in the catalyst in any amount which iscatalytically effective, with good results obtained with about 0.1 toabout 5 mass-% indium on an elemental basis in the catalyst. Bestresults are ordinarily achieved with about 0.2 to about 2 mass-% indium,calculated on an elemental basis. The preferred atomic ratio of indiumto platinum group metal for this catalyst is at least about 2:1,preferably about 1.5:1 or greater, and especially from about 3:1 ormore.

An indium component is incorporated in the catalytic composite in anysuitable manner known to the art, such as by coprecipitation, cogelationor coextrusion with the porous carrier material, ion exchange with thegelled carrier material, or impregnation of the porous carrier materialeither after, before, or during the period when it is dried andcalcined. It is intended to include within the scope of the presentinvention all conventional methods for incorporating and simultaneouslydistributing a metallic component in a catalytic composite in a desiredmanner, as the particular method of incorporation used is not deemed tobe an essential feature of the present invention. Preferably the methodused results in a relatively uniform dispersion of the indium moiety inthe carrier material.

One suitable method of incorporating indium into the catalytic compositeinvolves cogelling or coprecipitating the indium component in the formof the corresponding hydrous oxide or oxyhalide during the preparationof the preferred carrier material, alumina. This method typicallyinvolves the addition of a suitable sol-soluble or sol-dispersibleindium compound such as the indium trichloride, indium oxide, and thelike to the alumina hydrosol and then combining the indium-containinghydrosol with a suitable gelling agent and dropping the resultingmixture into an oil bath, etc., as explained in detail hereinbefore.Alternatively, the indium compound can be added to the gelling agent.After drying and calcining the resulting gelled carrier material in air,an intimate combination of alumina and indium oxide and/or oxychlorideis obtained.

Another effective method of incorporating the indium into the catalyticcomposite involves utilization of a soluble, decomposable compound ofindium in solution to impregnate the porous carrier material. Ingeneral, the solvent used in this impregnation step is selected on thebasis of the capability to dissolve the desired indium compound and tohold it in solution until it is evenly distributed throughout thecarrier material without adversely affecting the carrier material or theother ingredients of the catalyst. Suitable solvents comprise alcohols,ethers, acids, and the like, with an aqueous, acidic solution beingpreferred. Thus, the indium component may be added to the carriermaterial by commingling the carrier with an aqueous acidic solution ofsuitable indium salt, complex, or compound such as a nitrate, chloride,fluoride, organic alkyl, hydroxide, oxide, and the like compounds.Suitable acids for use in the impregnation solution are: inorganic acidssuch as hydrochloric acid, nitric acid, and the like, and stronglyacidic organic acids such as oxalic acid, malonic acid, citric acid, andthe like. The indium component can be impregnated into the carriereither prior to, simultaneously with, or after the platinum-group metalcomponent.

A Group IVA(IUPAC 14) metal component is an essential ingredient of thecatalyst of the present invention. Of the Group IVA metals, germaniumand tin are preferred and tin is especially preferred. This componentmay be present as an elemental metal, as a chemical compound such as theoxide, sulfide, halide, oxychloride, etc., or as a physical or chemicalcombination with the porous carrier material and/or other components ofthe catalytic composite. Preferably, a substantial portion of the GroupIVA metal exists in the finished catalyst in an oxidation state abovethat of the elemental metal. The Group IVA metal component optimally isutilized in an amount sufficient to result in a final catalyticcomposite containing about 0.01 to about 5 mass % metal, calculated onan elemental basis, with best results obtained at a level of about 0.1to about 2 mass-% metal.

The Group IVA(IUPAC 14) metal component may be incorporated in thecatalyst in any suitable manner to achieve a homogeneous dispersion,such as by coprecipitation with the porous carrier material,ion-exchange with the carrier material or impregnation of the carriermaterial at any stage in the preparation. One method of incorporatingthe Group IVA metal component into the catalyst composite involves theutilization of a soluble, decomposable compound of a Group IVA metal toimpregnate and disperse the metal throughout the porous carriermaterial. The Group IVA metal component can be impregnated either priorto, simultaneously with, or after the other components are added to thecarrier material. Thus, the Group IVA metal component may be added tothe carrier material by commingling the latter with an aqueous solutionof a suitable metal salt or soluble compound such as stannous bromide,stannous chloride, stannic chloride, stannic chloride pentahydrate; orgermanium oxide, germanium tetraethoxide, germanium tetrachloride; orlead nitrate, lead acetate, lead chlorate and the like compounds. Theutilization of Group IVA metal chloride compounds, such as stannicchloride, germanium tetrachloride or lead chlorate is particularlypreferred since it facilitates the incorporation of both the metalcomponent and at least a minor amount of the preferred halogen componentin a single step. When combined with hydrogen chloride during theespecially preferred alumina peptization step described hereinabove, ahomogeneous dispersion of the Group IVA metal component is obtained inaccordance with the present invention. In an alternative embodiment,organic metal compounds such as trimethyltin chloride and dimethyltindichloride are incorporated into the catalyst during the peptization ofthe inorganic oxide binder, and most preferably during peptization ofalumina with hydrogen chloride or nitric acid.

A surface-layer platinum-group metal component is an essential componentof the present catalyst. Of the platinum-group metals, i.e., platinum,palladium, rhodium, ruthenium, osmium and iridium, palladium is apreferred component and platinum is especially preferred. Mixtures ofplatinum-group metals also are within the scope of this invention. Thiscomponent may exist within the final catalytic composite as a compoundsuch as an oxide, sulfide, halide, or oxyhalide, in chemical combinationwith one or more of the other ingredients of the composite, or as anelemental metal. Best results are obtained when substantially all ofthis component is present in the elemental state. This component may bepresent in the final catalyst composite in any amount which iscatalytically effective, but relatively small amounts are preferred. Infact, the surface-layer platinum-group metal component generally willcomprise about 0.01 to 2 mass-% of the final catalyst, calculated on anelemental basis. Excellent results are obtained when the catalystcontains about 0.05 to 1 mass-% of platinum.

An essential feature of the catalyst of the present invention,therefore, is that the platinum-group metal component is concentrated inthe surface layer of each catalyst particle. "Layer" is a stratum of thecatalyst particle of substantially uniform thickness. The "surfacelayer" is the layer of the catalyst particle adjacent to the externalsurface of the particle. "Diameter" is defined as the minimum regulardimension through the center of the catalyst particle; for example, thisdimension would be the diameter of the cylinder of an extrudate."Radius" is defined as the distance from the surface to the center ofthe catalyst particle, being half of the diameter of the particle. Asexemplified hereinbelow, the surface layer comprises a layer extending50 to 100 microns into the catalyst particle from the external surfaceof the particle; within the preferred range of particle sizes, thesurface layer is usefully measured at a depth of 100 microns for acatalyst particle having a diameter of from about 1.2 to 3.5 mm, and ata depth of 50 microns for particles in the 0.7 to 2 mm range. A centralcore is measured as a portion surrounding the center of the particle andcorresponding 50% of the diameter of the particle. "Central core" isdefined in the present invention as a concentric cylindrical orspherical portion of a cylindrical or spherical catalyst particle,respectively, having a diameter that is 50% of the diameter of thecatalyst particle. For the alternative extrudate particles, the centralcore is a concentric cylindrical portion excluding the surface layer atthe ends of the extrudate particles. Other quantitative criteriarelating to the definition of a surface layer and central core are notexcluded by these specific definitions.

The characterization of the platinum-group metal component as a"surface-layer" component is intended to encompass a platinum-groupmetal component gradient upon and within the catalyst support. Theconcentration of platinum-group metal component tapers off, generallyvery sharply, in progressing from the surface to the center of thecatalyst particle. The actual gradient of the platinum-group metalcomponent within the catalyst particle varies depending upon themanufacturing method used to fabricate the catalyst. Optimally about 50%or more of the surface-layer platinum-group metal is contained in the100-micron surface layer of the catalyst. Alternatively, the definitionmay be stated as 40% or more of the surface-layer metal being containedin the 50-micron surface layer of the catalyst. Preferably theconcentration of the platinum-group metal component in the surface layerof the catalyst is at least twice, more preferably at least five times,and most preferably at least ten times, the concentration in the centralcore of the catalyst particle.

The gradient of the Group VIII noble metals preferably is determined byScanning Electron Microscopy ("SEM"). SEM determinations of local metalconcentrations are effected on at least three sample particles from abed of catalyst particles. Particle samples are selected from the bed bytechniques known to those of ordinary skill in the art. The SEM datashow the approximate metals content of any one point within the catalystpill, based on the metals distribution profile in relation to thealumina level. The result of each analysis may not be based upon a zeropoint. The entire curve could be shifted either up or down, and thevalue of the integrated distribution curve therefore does not relatedirectly to the measured average concentration. The data thus are usefulfor evaluating and comparing the distribution of metals but not indetermining overall metal contents.

A metal, such as the indium or Group IVA(IUPAC 14) components describedhereinbefore, is considered uniformly dispersed if no clear pattern ofmetal distribution is apparent between the external surface and thecenter of catalyst particles. More specifically, uniform dispersion maybe defined by the standard deviation of metal concentrations at five ormore strata derived from determinations on three or more particles beingless than about 25% of the average SEM-determined concentration on theparticles. Preferably, the standard deviation of the uniformly dispersedmetal concentration is less than about 15% of the average SEM-determinedconcentration on the particles.

Typical but non-limiting platinum-group metal compounds which may beemployed in preparing the surface-layer platinum component of thecatalyst of the invention include chloroplatinic acid, ammoniumchloroplatinate, bromoplatinic acid, platinum dichloride, platinumtetrachloride hydrate, platinum dichlorocarbonyl dichloride,dinitrodiaminoplatinum, palladium chloride, palladium chloridedihydrate, palladium nitrate, etc., and analogous compounds of the otherplatinum-group metals. Chloroplatinic acid or tetraamine platinumchloride are preferred compounds of the preferred platinum component.

The platinum-group metal component may be incorporated into the catalystof the present invention by any means suitable to result in asurface-layer component, and the methods described hereinafter are notintended to limit the scope of the invention. One suitable methodinvolves surface-impregnating the platinum-group component by means of alow-acid impregnation utilizing a solution of a soluble, decomposablecomplex compound of the platinum group component. In general the solventused in this impregnation step is selected on the basis of itscapability to dissolve the desired decomposable complex compound and isa low-acid, preferably aqueous solution. By low-acid it is meant thatthe impregnation solution generally has a normality of 2 or less. Asurface-layer platinum-group metal component may be impregnated onto thecatalyst from a solution of chloroplatinic acid in the absence of strongmineral acids such as hydrochloric and nitric acid.

The surface-layer platinum-group metal component alternatively may beincorporated into the catalyst by spray impregnation. For example, acatalytic support as described hereinbefore is placed into a rotatingdrum which contains a spray nozzle. A solution of the salt of thesurface-layer metal is ejected from the nozzle using air to form finedroplets of spray, which contact the support in the rotating drum foreffective mixing. The volume ratio of solution to support is sufficientto effect the desired concentration of surface-layer metal in thecatalyst, but generally less than the catalyst pore volume andpreferably amounts to about 5 to about 50% of the pore volume. Thecatalyst composite in the drum is rolled for a period of from about 0.1to 12 hours, preferably from about 0.1 to 1 hour, and dried for about0.2 to 12 hours at a temperature of between about 150 and 250° C.

Alternatively, the platinum-group metal component may be surfaceimpregnated via the formulation of a chemical complex of theplatinum-group metal component which is strongly attracted to therefractory oxide support, resulting in the platinum group metal beingretained primarily upon the outer surface of the catalyst. Any compoundthat is known to complex with the desired platinum-group component andwith the metal component of the refractory inorganic-oxide support maybe used in the preparation of the catalyst of the present invention. Ithas been found that a multi-dentated ligand is very useful in complexingwith a platinum group metal and the refractory inorganic oxide support,resulting in surface-impregnation of the platinum-group metal component.Multi-dentated ligands are compounds that contain more than oneappendage that can bond strongly to the oxide support. For example, themulti-dentated ligand may contain a functional group such as --SH or PR₂(where R is hydrocarbon) that has a high affinity towards the platinumgroup metal component and a second functional group comprising acomponent that can be strongly adsorbed onto the metal oxide support.Such appendages would typically comprise carboxylic acids, amino groups,thiol groups, phosphorus groups, or other strongly polar groups ofchemical components. This property of the multi-dentated ligandeffectively ensures that the platinum group metal component does notpenetrate the catalyst particle, by binding strongly with the platinumgroup metal while also binding to the support quickly and strongly.Examples of some useful multi-dentated ligands include thiomalic acid(TMA), thiolactic acid, mercaptopropionic acid, thiodiacetic acid,thioglycolic acid, and thiopropionic acid among others.

Other non-limiting methods include the use of materials which physicallyprevent the penetration of the platinum-group metal component into theinterior of the catalyst particle, such as the nonionic surface-activeagent of the poly(oxyethylene) type of U.S. Pat. No. 3,897,368.

Optionally the catalyst may also contain other components or mixturesthereof which act alone or in concert as catalyst modifiers to improveactivity, selectivity or stability. Some known catalyst modifiersinclude rhenium, cobalt, nickel, iron, tungsten, molybdenum, chromium,bismuth, antimony, zinc, cadmium, copper and one or more of thelanthanides. Catalytically effective amounts of these components may beadded in any suitable manner to the carrier material during or after itspreparation or to the catalytic composite before, while or after othercomponents are being incorporated.

An optional component of the catalyst, particularly useful inhydrocarbon conversion embodiments of the present invention comprisingdehydrogenation, dehydrocyclization, or hydrogenation reactions, is analkali or alkaline-earth metal component. More precisely, this optionalingredient is selected from the group consisting of the compounds of thealkali metals--cesium, rubidium, potassium, sodium, and lithium--and thecompounds of the alkaline earth metals--calcium, strontium, barium, andmagnesium. Good results are obtained in these embodiments when thiscomponent, if present, constitutes about 0.01 to about 5 mass-% of thecomposite, calculated on an elemental basis. This optional alkali oralkaline earth metal component can be incorporated into the composite inany of the known ways with impregnation with an aqueous solution of asuitable water-soluble, decomposable compound being preferred.

It is necessary to employ at least one oxidation step in the preparationof the catalyst. The conditions employed to effect the oxidation stepare selected to convert substantially all of the metallic componentswithin the catalytic composite to their corresponding oxide form. Theoxidation step typically takes place at oxidation conditions comprisinga temperature of from about 370° to about 600° C. An oxygen atmosphereis employed which typically comprises air. Generally, the oxidation stepwill be carried out for a period of from about 0.5 to about 10 hours ormore, the exact period of time being that required to convertsubstantially all of the metallic components to their correspondingoxide form. This time will, of course, vary with the oxidationtemperature employed and the oxygen content of the atmosphere employed.

The catalyst usually comprises a halogen component, with chlorine beingthe preferred halogen. The halogen may be introduced in the preparationof the support and/or the incorporation of metal components into thecatalyst, or added as an acid such as HCl or HF or a salt. Ahalogen-adjustment step may also be employed in preparing the catalystwhich may serve the dual function of aiding in homogeneous dispersion ofa metal component as well as a means of incorporating the desired levelof halogen into the final catalytic composite. In the preferred chlorineembodiment, the preferred halogen or halogen-containing compoundutilized during the halogen adjustment step is chlorine, HCl orprecursor of these compounds. In carrying out the halogen-adjustmentstep, the catalytic composite is contacted with the halogen orhalogen-containing compound in air or an oxygen atmosphere at anelevated temperature of from about 370° to about 600° C. for a period ofabout 0.5 to 5 hours or more. Water preferably is present in a moleratio of water to HCl of about 5:1 to about 100:1. Irrespective of thedetails of the halogen-adjustment step employed, the halogen content ofthe final catalyst should comprise, on an elemental basis, from about0.1 to about 10 mass-% of the finished composite.

In preparing the catalyst, it generally is also necessary to employ areduction step. The reduction step is designed to reduce substantiallyall of the platinum-group metal component to the corresponding elementalmetallic state and to ensure a relatively uniform and finely divideddispersion of this component within the surface layer of the catalyticcomposite. It is preferred that the reduction step take place in asubstantially water-free environment. Preferably, the reducing gas issubstantially pure, dry hydrogen (i.e., less than 20 volume ppm water).However, other reducing gases may be employed such as CO, nitrogen, etc.Typically, the reducing gas is contacted with the oxidized catalyticcomposite at reduction conditions including a reduction temperature offrom about 315° to about 650° C. for a period of time of from about 0.5to 10 or more hours effective to reduce substantially all of theplatinum-group metal component to the elemental metallic state. Thereduction step may be performed prior to loading the catalytic compositeinto the hydrocarbon conversion zone or it may be performed in situ aspart of a hydrocarbon conversion process start-up procedure. However, ifthis latter technique is employed, proper precautions must be taken topredry the hydrocarbon conversion plant to a substantially water-freestate and a substantially water-free hydrogen-containing reduction gasshould be employed.

Optionally, the catalytic composite may be subjected to a presulfidingstep. The optional sulfur component may be incorporated into thecatalyst by any suitable technique known in the art.

The catalyst of the present invention has particular utility as ahydrocarbon conversion catalyst. The hydrocarbon which is to beconverted is contacted with the catalyst at hydrocarbon-conversionconditions, which include a temperature of from 40° to 300° C., apressure of from atmospheric to 200 atmospheres absolute and liquidhourly space velocities from about 0.1 to 100 hr⁻¹. The catalyst isparticularly suitable for catalytic reforming of gasoline-rangefeedstocks, and also may be used for dehydrocyclization, isomerizationof aliphatics and aromatics, dehydrogenation, hydrocracking,disproportionation, dealkylation, alkylation, transalkylation,oligomerization, and other hydrocarbon conversions.

In the preferred catalytic reforming embodiment, hydrocarbon feedstockand a hydrogen-rich gas are preheated and charged to a reforming zonecontaining typically two to five reactors in series. Suitable heatingmeans are provided between reactors to compensate for the netendothermic heat of reaction in each of the reactors. The reactants maycontact the catalyst in individual reactors in either upflow, downflow,or radial flow fashion, with the radial flow mode being preferred. Thecatalyst is contained in a fixed-bed system or, preferably, in amoving-bed system with associated continuous catalyst regeneration.Alternative approaches to reactivation of deactivated catalyst are wellknown to those skilled in the art, and include semiregenerativeoperation in which the entire unit is shut down for catalystregeneration and reactivation or swing-reactor operation in which anindividual reactor is isolated from the system, regenerated andreactivated while the other reactors remain on-stream. The preferredcontinuous catalyst regeneration in conjunction with a moving-bed systemis disclosed, inter alia, in U.S. Pat. Nos. 3,647,680; 3,652,231;3,692,496; and 4,832,291, all of which are incorporated herein byreference.

Effluent from the reforming zone is passed through a cooling means to aseparation zone, typically maintained at about 0° to 65° C., wherein ahydrogen-rich gas is separated from a liquid stream commonly called"unstabilized reformate". The resultant hydrogen stream can then berecycled through suitable compressing means back to the reforming zone.The liquid phase from the separation zone is typically withdrawn andprocessed in a fractionating system in order to adjust the butaneconcentration, thereby controlling front-end volatility of the resultingreformate.

Operating conditions applied in the reforming process of the presentinvention include a pressure selected within the range of about 100 kPato 7 MPa (abs). Particularly good results are obtained at low pressure,namely a pressure of about 350 to 2500 kPa (abs). Reforming temperatureis in the range from about 315° to 600° C., and preferably from about425° to 565° C. As is well known to those skilled in the reforming art,the initial selection of the temperature within this broad range is madeprimarily as a function of the desired octane of the product reformateconsidering the characteristics of the charge stock and of the catalyst.Ordinarily, the temperature then is thereafter slowly increased duringthe run to compensate for the inevitable deactivation that occurs toprovide a constant octane product. Sufficient hydrogen is supplied toprovide an amount of about 1 to about 20 moles of hydrogen per mole ofhydrocarbon feed entering the reforming zone, with excellent resultsbeing obtained when about 2 to about 10 moles of hydrogen are used permole of hydrocarbon feed. Likewise, the liquid hourly space velocity(LHSV) used in reforming is selected from the range of about 0.1 toabout 10 hr⁻¹, with a value in the range of about 1 to about 5 hr⁻¹being preferred.

The hydrocarbon feedstock that is charged to this reforming systempreferably is a naphtha feedstock comprising naphthenes and paraffinsthat boil within the gasoline range. The preferred feedstocks arenaphthas consisting principally of naphthenes and paraffins, although,in many cases, aromatics also will be present. This preferred classincludes straight-run gasolines, natural gasolines, synthetic gasolines,and the like. As an alternative embodiment, it is frequentlyadvantageous to charge thermally or catalytically cracked gasolines,partially reformed naphthas, or dehydrogenated naphthas. Mixtures ofstraight-run and cracked gasoline-range naphthas can also be used toadvantage. The gasoline-range naphtha charge stock may be a full-boilinggasoline having an initial ASTM D-86 boiling point of from about 40-80°C. and an end boiling point within the range of from about 160-220° C.,or may be a selected fraction thereof which generally will be ahigher-boiling fraction commonly referred to as a heavy naphtha--forexample, a naphtha boiling in the range of 100-200° C. If the reformingis directed to production of one or more of benzene, toluene andxylenes, the boiling range may be principally or substantially withinthe range of 60°-150° C. In some cases, it is also advantageous tocharge to the process pure hydrocarbons or mixtures of hydrocarbons thathave been recovered from extraction units--for example, raffinates fromaromatics extraction or straight-chain paraffins derived from adsorptionprocesses--of which a substantial portion are converted to aromaticsaccording to the present process.

It is generally preferred to utilize the present invention in asubstantially water-free environment. Essential to the achievement ofthis condition in the reforming zone is the control of the water levelpresent in the feedstock and the hydrogen stream which is being chargedto the zone. Best results are ordinarily obtained when the total amountof water entering the conversion zone from any source is held to a levelless than 50 ppm and preferably less than 20 ppm, expressed as weight ofequivalent water in the feedstock. In general, this can be accomplishedby careful control of the water present in the feedstock and in thehydrogen stream. The feedstock can be dried by using any suitable dryingmeans known to the art such as a conventional solid adsorbent having ahigh selectivity for water; for instance, sodium or calcium crystallinealuminosilicates, silica gel, activated alumina, molecular sieves,anhydrous calcium sulfate, high surface area sodium, and the likeadsorbents. Similarly, the water content of the feedstock may beadjusted by suitable stripping operations in a fractionation column orlike device. In some cases, a combination of adsorbent drying anddistillation drying may be used advantageously to effect almost completeremoval of water from the feedstock. Preferably, the feedstock is driedto a level corresponding to less than 20 ppm of H₂ O equivalent.

It is preferred concomitantly to maintain the water content of thehydrogen stream entering the hydrocarbon conversion zone at a level ofabout 10 to about 20 volume ppm or less. In the cases where the watercontent of the hydrogen stream is above this range, this can beconveniently accomplished by contacting the hydrogen stream with asuitable desiccant such as those mentioned above at conventional dryingconditions.

It is a preferred practice to use the present invention in asubstantially sulfur-free environment. Any control means known in theart may be used to treat the naphtha feedstock which is to be charged tothe reforming reaction zone. For example, the feedstock may be subjectedto adsorption processes, catalytic processes, or combinations thereof.Adsorption processes may employ molecular sieves, high surface areasilica-aluminas, carbon molecular sieves, crystalline aluminosilicates,activated carbons, high surface area metal-containing compositions, suchas Ni or Cu and the like. Feedstocks preferably are treated byconventional catalytic pretreatment methods such as hydrorefining,hydrotreating, hydrodesulfurization, etc., to remove substantially allsulfurous, nitrogenous and water-yielding contaminants therefrom, and tosaturate any olefins that may be contained therein. Catalytic processesmay employ traditional sulfur reducing catalyst formulations known tothe art including refractory inorganic oxide supports containing metalsselected from the group comprising Group VI-B(IUPAC 6), Group II-B(IUPAC12), and Group VIII(IUPAC 8-10) of the Periodic Table.

The following examples are presented to elucidate the catalyst andprocess of the present invention, demonstrating selectivity advantagesover prior-art technology. These examples are offered as illustrativeembodiments and should not be interpreted as limiting the claims.

EXAMPLE I

The advantages of the invention are illustrated through characterizationand performance data for Catalysts A, B and C relative to Catalysts X, Yand Z, respectively, as described hereinbelow. Three particles of eachcatalyst were tested for metals distribution. Catalysts A, B and Ccomprise platinum and tin without indium, while Catalysts X, Y and Zcomprise platinum, tin and indium. Catalysts A and X comprise uniformlydistributed platinum, while Catalysts B, C, Y and Z comprisesurface-layer platinum. In the examples presented hereinbelow, platinumconcentration is measured from the surface to the center, or over theradius, of the catalyst particle.

EXAMPLE II

A spherical catalyst of the prior art comprising tin and uniformlydispersed platinum on an alumina support was prepared by conventionaltechniques as a control catalyst for performance tests in comparisonwith catalysts of the invention. Tin was incorporated into alumina solaccording to the prior art by commingling a tin component with aluminumhydrosol. The tin-containing alumina sol was oil-dropped to form 1.6 mmspheres which were steamed to dryness at about 10% LOI and calcined at650° C. with 3% steam. The resulting calcined composite was impregnatedwith chloroplatinic acid in HCl to provide 0.38 mass-% Pt in thefinished catalyst. The impregnated catalyst was dried and oxychlorinatedat 525° C. with 2M HCl in air and reduced with pure H₂ at 565° C. Thefinished control catalyst was designated as Catalyst A and had thefollowing approximate composition in mass-%:

    ______________________________________                                                Tin    0.3                                                                    Platinum                                                                             0.38                                                                   Chloride                                                                             1.1                                                            ______________________________________                                    

EXAMPLE III

A spherical catalyst of the prior art comprising tin and uniformlydispersed platinum on an alumina support was prepared by conventionaltechniques as a control catalyst for performance tests in comparisonwith catalysts of the invention. Tin-containing alumina sol wasoil-dropped to form 1.6 mm spheres steamed to dryness at about 10% LOIand calcined at 650° C. as in Example II. The spherical support then wasimpregnated with indium chloride in HCl and oxychlorinated at 525° C.The resulting composite was impregnated with chloroplatinic acid in HClto provide 0.38 mass-% Pt in the finished catalyst. The impregnatedcatalyst was dried and oxychlorinated at 525° C. with 2M HCl in air andreduced with pure H₂ at 565° C.

The finished In-containing control catalyst was designated as Catalyst Xand had the following approximate composition in mass-%:

    ______________________________________                                                Indium 0.76                                                                   Tin    0.3                                                                    Platinum                                                                             0.38                                                                   Chloride                                                                             1.3                                                            ______________________________________                                    

EXAMPLE IV

Catalysts A and X were evaluated by Scanning Election Microscopy (SEM).The purpose of this analysis was to identify the relative distributionof platinum across the radius of particles of the catalyst, as well asto examine the distribution of tin. Three particles each of A and X wereevaluated in order to provide reliable average data.

The SEM data shows the approximate metals content of any one pointwithin the catalyst pill, as indicated hereinabove, based on the metalsdistribution profile in relation to the support. The data are useful fordetermining relative concentrations of metals across the catalystparticles, but do not necessarily represent accurate absolute values.

FIG. 1 shows the distribution of platinum and tin across the 800-micronradius of the spherical particles of Catalyst A from the surface to thecenter of each particle. Catalyst A displayed a relatively evendistribution of both platinum and tin across the catalyst particles,with no discernable trend in concentration and greater variation amongthe three catalyst particles tested than in relative concentrations indifferent layers of the particles. Less than about 25% of the platinumor tin is concentrated in the 50-micron surface layer of the particle,and less than about 40% is in the 100-micron surface layer.

FIG. 2 shows the distribution of platinum and tin across the 800-micronradius of the spherical particles of Catalyst X from the surface to thecenter of each particle. Catalyst X displayed a relatively evendistribution of platinum, indium and tin across the catalyst particles,with no discernable trend in concentration and greater variation amongthe three catalyst particles tested than in relative concentrations indifferent layers of the particles. Less than about 25% of the platinum,indium or tin is concentrated in the 50-micron surface layer of theparticle, and less than about 40% is in the 100-micron surface layer.

EXAMPLE V

Pilot-plant tests were structured to compare the selectivity to C₅ +product in reforming a naphtha feedstock when utilizing Catalysts A andX. The tests were based on reforming naphtha over the catalysts at apressure of 0.8 MPa (abs), liquid hourly space velocity of 3 hr⁻¹, andhydrogen/hydrocarbon mol ratio of 8. A range of conversion was studiedby varying temperature to provide data points at 502° C., 512° C., 522°C., and 532° C. The naphtha for the comparative tests was a hydrotreatedpetroleum-derived naphtha derived from a paraffinic mid-continent crudeoil which had the following characteristics:

    ______________________________________                                        Specific gravity    0.737                                                     Distillation, ASTM D-86, ° C.                                          IBP                 87                                                        10%                 97                                                        50%                 116                                                       90%                 140                                                       EP                  159                                                       Mass-%                                                                        paraffins           60                                                        naphthenes          27                                                        aromatics           13                                                        ______________________________________                                    

The results are shown in FIG. 3 as C₅ + yield vs. conversion ofparaffins and naphthenes for Catalysts A and X. Since a high C₅ + yieldindicates the efficiency of production of gasoline-range components fromthe feedstock, C₅ + yield is an indication of high selectivity.Indium-containing Catalyst X shows a C₅ + yield advantage of about 0.9mass-% over Catalyst A in the 75-85% conversion range.

EXAMPLE VI

Two composites were prepared in the same manner as Catalyst A throughsteps of incorporating tin into alumina and calcination. The compositesthen were processed as follows to incorporate a surface-layer platinumcomponent into the finished catalyst.

Catalyst B was prepared by spray impregnation of a platinum componentonto the tin-containing alumina spheres. The spheres were tumbled in adrum while a solution of chloroplatinic acid was pumped though a spraynozzle for about 15-20 minutes. The solution volume amounted to about25% of the pore volume of the catalyst and comprised sufficient platinumcomponent to provide 0.27 mass-% Pt in the finished catalyst. Afterrolling was completed, the spray-impregnated catalyst was dried for 2hours at about 180° C., oxychlorinated at 525° C. with 2M HCl in air andreduced with pure H₂ at 565° C.

Catalyst C was prepared using a multi-dentated ligand, thiomalic acid(TMA), to effect surface-layer platinum in an amount of about 0,25mass-% on the finished catalyst. The tin-containing alumina spheres werecontacted with a solution of thiomalic acid and chloroplatinic acid in arotary evaporator, cold-rolled for 30 minutes, and the solution wasevaporated with steam. The resulting catalyst was dried, steamed for 3hr at 525° C., oxychlorinated at 525° C. with 2M HCl in air and reducedwith pure H₂ at 565° C.

The catalysts had the following respective compositions in mass-%:

    ______________________________________                                        Catalyst:        B      C                                                     ______________________________________                                        Tin              0.32   0.60                                                  Platinum         0.27   0.25                                                  Chloride         1.2    1.3                                                   ______________________________________                                    

EXAMPLE VII

Catalyst Y of the invention was prepared in the same manner as thecontrol Catalyst X through steps of incorporating tin into alumina andimpregnation of an indium component, and then was calcined at 650° C.with 3% steam. The composite then was processed as follows toincorporate surface-layer platinum by spray impregnation of a platinumcomponent onto the tin- and indium-containing alumina spheres. Thespheres were tumbled in a drum while being sprayed with a solution ofchloroplatinic acid in HCl to provide 0.25 mass-% Pt in the finishedcatalyst. The spray-impregnated catalyst was dried, oxychlorinated at525° C. with 2M HCl in air and reduced with pure H₂ at 565° C.

Catalyst Z was prepared using a multi-dentated ligand, thiomalic acid(TMA), to effect surface-layer platinum. Tin and indium wereincorporated into alumina spheres by commingling tin chloride and indiumchloride with aluminum hydrosol and oil-dropping the sol to form sphereswhich were steamed to dryness at about 10% LOI and calcined at 650° C.The tin- and indium-containing alumina spheres were contacted with asolution of thiomalic acid and chloroplatinic acid in a rotaryevaporator, cold-rolled for 30 minutes, and the solution was evaporatedwith steam. The resulting catalyst was dried, steamed for 3 hr at 525°C., oxychlorinated at 525° C. with 2M HCl in air and reduced with pureH₂ at 565° C.

The catalysts had the following respective compositions in mass-%:

    ______________________________________                                        Catalyst:        Y      Z                                                     ______________________________________                                        Indium           0.78   0.77                                                  Tin              0.3    0.61                                                  Platinum         0.25   0.25                                                  Chloride         1.1    1.3                                                   ______________________________________                                    

EXAMPLE VIII

Catalysts B, C, Y and Z were evaluated by Scanning Election Microscopy(SEM). The purpose of this analysis was to identify the relativedistribution of platinum across the radius of particles of the catalyst,as well as to examine the distribution of tin and, for catalysts Y andZ, indium. Three particles each of B, C, Y and Z were evaluated in orderto provide reliable average data.

The SEM data shows the approximate metals content of any one pointwithin the catalyst pill, as indicated hereinabove, based on the metalsdistribution profile in relation to the support. The data are useful fordetermining relative concentrations of metals across the catalystparticles, but do not necessarily represent accurate absolute values.

FIGS. 4, 5, 6 and 7 shows distribution of platinum, indium and tinacross the radius of the catalyst particles respectively for CatalystsB, C, Y and Z. All of the catalysts show an exceptionally highconcentration of platinum on a relative basis in the surface layer ofthe catalyst particles, and thus are suitable for considering the effectof adding indium to reforming catalysts containing surface-layerplatinum. The catalysts displayed a relatively even distribution of tinand indium when present across the catalyst particles, consistent withthe distribution in Catalysts A and X, with no discernable trend inconcentration.

To quantify the differences between the catalysts of the invention andof the prior art, the relative proportions of platinum in surface layerswere calculated from the data presented in FIG. 1. The 100-micronsurface layer represents about one-third of the volume of the sphericalparticle, while the 50-micron surface layer represents about 171/2% ofthe volume of the particle. The proportion of the platinum in theaverage particle (of 3 determinations) which is contained in the100-micron and 50-micron surface layer was calculated, and theconcentration in the surface layers was related to the concentration inthe central core. These criteria relating to platinum in the surfacelayer indicates that platinum is concentrated near the surface of theparticles while indium and tin are uniformly dispersed:

    ______________________________________                                        Catalyst:        B      C        Y    Z                                       ______________________________________                                        % of Pt in 100μ surface layer                                                               94     55       99   83                                      % of Pt in 50μ surface layer                                                                79     42       94   60                                      % Pt in 100μ layer/% in core                                                                10.5   870      460  250                                     % Pt in 100μ layer/% in core                                                                16.5   1250     820  330                                     Std. deviation of In conc.*                                                                    --     --       10   8                                       Std. deviation of Sn conc.*                                                                    23     10       18   13                                      ______________________________________                                         *Standard deviation of concentration as % of average value in particle   

EXAMPLE IX

Pilot-plant tests were structured to compare the selectivity to C₅ +product in reforming a naphtha feedstock when utilizing Catalysts B vs.Y and C vs. Z. The tests were based on reforming naphtha over thecatalysts at a pressure of 0.8 MPa (abs), liquid hourly space velocityof 3 hr⁻¹, and hydrogen/hydrocarbon mol ratio of 8. A range ofconversion was studied by varying temperature to provide data points at502° C., 512° C., 522° C., and 532° C. The naphtha for the comparativetests was the same naphtha use in the tests described in Example V:

    ______________________________________                                        Specific gravity    0.737                                                     Distillation, ASTM D-86, ° C.                                          IBP                 87                                                        10%                 97                                                        50%                 116                                                       90%                 140                                                       EP                  159                                                       Mass-%                                                                        paraffins           60                                                        naphthenes          27                                                        aromatics           13                                                        ______________________________________                                    

The results are shown in FIG. 8 as C₅ + yield vs. conversion ofparaffins and naphthenes for Catalysts B and Y and in FIG. 9 as C₅ +yield vs. conversion for Catalysts C and Z. Since a high C₅ + yieldindicates the efficiency of production of gasoline-range components fromthe feedstock, C₅ + yield is an indication of high selectivity. Therespective indium-containing catalysts demonstrate improvements in suchselectivity over catalysts not containing indium. Recalling also theresults in Example V, the relative C₅ + yield advantages in the 75-85%conversion range are as follows in mass-%:

    ______________________________________                                        Catalysts           ΔC.sub.5 +                                          ______________________________________                                        X vs. A (uniform Pt)                                                                              0.9                                                       Y vs. B (spray impregnation)                                                                      2.7                                                       Z vs. C (TMA impregnation)                                                                        2.2                                                       ______________________________________                                    

Indium modification is clearly more advantageous with respect to thereforming catalysts containing surface-layer platinum.

We claim:
 1. A process for the catalytic reforming of a naphthafeedstock which comprises contacting the feedstock at reformingconditions including a temperature of about 425° to 565° C., a pressureof about 350 to 2500 kPa (ga), a liquid hourly space velocity of about 1to 5 hr⁻¹, and a mole ratio of hydrogen to hydrocarbon feed of about 2to 10, with a dual-function catalyst comprising a combination of arefractory inorganic oxide support with a multigradient metal componentcomprising about
 0. 1 to 5 mass-% on an elemental basis of a uniformlydispersed indium component, about 0.01 to 5 mass-% on an elemental basisof a uniformly dispersed Group IVA (IUPAC 14) metal component, fromabout 0.1 to 10 mass-% on an elemental basis of a halogen component andabout 0.01 to 2 mass-% on an elemental basis of a platinum-group metalcomponent wherein particles of the catalyst are characterized ascontaining about 40% or more of the platinum-group metal in a 50-micronsurface layer of the particles and the concentration of theplatinum-group metal in the 50-micron surface layer of the particles isat least five times the concentration of the platinum-group metal in acentral core having a diameter that is 50% of the diameter of theparticles.
 2. The process of claim 1 wherein the refractory inorganicoxide comprises alumina.
 3. The process of claim 1 wherein the GroupIVA(IUPAC 14) metal component comprises a tin component.
 4. The processof claim 1 wherein the halogen comprises chlorine.
 5. The process ofclaim 1 wherein the atomic ratio of indium to platinum-group metal is atleast about 1.5.
 6. The process of claim 1 wherein the atomic ratio ofindium to platinum-group metal is at least about
 3. 7. The process ofclaim 1 wherein the platinum-group metal component comprises a platinumcomponent.